Flash-memory technologies such as those using electrically-erasable programmable read-only memory (EEPROM) have produced chips storing 1 G-Bytes or more. Small flash-memory cards have been designed that have a connector that can plug into a specialized reader, such as for compact-flash, secure-digital, memory stick, or other standardized formats.
More recently, flash memory cards are being sold that contain a USB connector. Such USB-flash memory cards do not require a specialized reader but can be plugged into a USB connector on a personal computer (PC) or other hosting device. These USB-flash memory cards can be used in place of floppy disks. A USB-flash card can have a capacity of more than ten floppy disks in an area not much larger than a large postage stamp.
FIG. 1A shows a prior-art flash-memory card with a USB connector. Flash memory chip 12 may be a 128 Mega-byte non-volatile chip or may have some other capacity. Controller chip 14 contains a flash-memory controller that generates signals to access memory locations within flash memory chip 12. Controller chip 14 also contains a USB interface controller that serially transfers data to and from flash memory chip 12 over a USB connection.
USB connector 20 may be mounted on board 10, which is a small circuit board with chips 12, 14 mounted thereon. Multi-layer printed-circuit board (PCB) technology can be used for board 10. A plastic case (not shown) can surround board 10.
USB connector 20 contains a small connector substrate 16, which is often white ceramic, black rigid plastic, or another sturdy substrate. Connector substrate 16 has four or more metal contacts 18 formed thereon. Metal contacts 18 carry the USB signals generated or received by controller chip 14. USB signals include power, ground, and serial differential data D+, D−.
USB connector 20 contains a metal case that wraps around connector substrate 16. The metal case touches connector substrate 16 on three of the sides of connector substrate 16. The top side of connector substrate 16, holding metal contacts 18, has a large gap to the top of the metal case. On the top and bottom of this metal wrap are formed holes 15. USB connector 20 is a male connector, such as a type-A USB connector.
FIG. 1B shows a female USB connector. Female USB connector 22 can be an integral part of a PC, or can be connected by cable 21. Another connector substrate 26 contains four metal contacts 28 that make electrical contact with the four metal contacts 18 of the male USB connector 20 of FIG. 1A. Connector substrate 26 is wrapped by a metal case, but small gaps are between the metal case and connector substrate 26 on the lower three sides.
Locking is provided by metal springs 24 in the top and bottom of the metal case. When male USB connector 20 of FIG. 1A is flipped over and inserted into Female USB connector 22 of FIG. 1B, metal springs 24 lock into holes 15 of male USB connector 20.
FIGS. 2A, 2B are cross-sections highlighting connections between male and female USB connectors. Female USB connector 22 is on the left while male USB connector 20 is being inserted from the right. Male USB connector 20 is flipped over relative to the view of FIG. 1A. Metal contacts 18 are formed on the lower surface of connector substrate 16 on male USB connector 20, while metal contacts 28 are formed on the upper surface of connector substrate 26 on Female USB connector 22. Thus the metal contacts face one another to allow for electrical contact when male USB connector 20 is inserted into Female USB connector 22 as shown in FIG. 2B.
Metal springs 24 formed on the metal case surrounding connector substrate 26 on Female USB connector 22 fit into holes on the metal case of male USB connector 20. This helps to lock the connectors together.
FIG. 3 shows a prior-art USB flash memory card using a slim USB connector. Male USB connector 20 of FIGS. 1, 2 is relatively large. The metal case in particular is cumbersome and increases manufacturing cost. Costs may be reduced by integrating male USB connector 30 with board 32. Board 32 is a PCB that has flash memory chip 12 and controller chip 14 mounted thereon. Board 32 is extended to include male USB connector 30, which has metal contacts 38 formed on end 36 of board 32.
The width and thickness of board 32 at end 36 containing male USB connector 30 is designed to approximately match that of connector substrate 16 of FIG. 1A. Plastic case 34 can enclose board 32 but have an opening for metal contacts 38. Plastic case 34 can cover the bottom and sides of male USB connector 30 up to end 36 to emulate potions of the metal case of the male USB connector of FIG. 1A.
FIGS. 4A, 4B show cross-sections of the prior-art slim USB connector being inserted into a standard Female USB connector. Board 32 that has male USB connector 30 formed on end 36 is flipped over from the view shown in FIG. 3, and end 36 is inserted into female USB connector 22 from the right side.
Metal contacts 38 are located on the lower surface of male USB connector 30. Plastic case 34 has an opening on the lower surface of male USB connector 30 to expose the metal contacts so they can make electrical connection with metal contacts 28 on the upper surface of connector substrate 26 of Female USB connector 22 when inserted as shown in FIG. 4B.
Plastic case 34 helps to fill the gate between board 32 and the top edge of the metal case of Female USB connector 22. Plastic case 34 is also formed along the thin edges of board 32 and helps to fill in the gaps between connector substrate 26 and the sides of the metal case of Female USB connector 22 that are above and below the plane of FIG. 4B.
While slim USB connector 30 can be less expensive and smaller than the standard USB connector, it fits less securely into a standard Female USB connector. The lack of the metal case removes the mechanical support provided as the male metal case that fit in the gap below connector substrate 26 and the bottom side of the metal case for the female connector. The result is a noticeable wobble in the up and down direction when a USB flash memory card containing male USB connector 30 is inserted into Female USB connector 22. Vertical movement of 3–4 millimeter at the end of a 4-centimeter flash card can occur with slight finger pressure. This vertical play gives the user the feeling that the flash memory card is cheap and unreliable, even when sufficient electrical contact is made.